The present invention relates to a blood sugar sensor and monitor, and more particularly to an implantable transducer capable of detecting variations in blood sugar level by detecting changes in blood osmotic pressure.
Among the therapeutic measures taken for controlling blood glucose concentration or values in patients subject to diabetes mellitus, insulin has been found particularly effective as a result of exerting a direct effect on glucose, protein and lipid metabolism. However, proper dosage of insulin injection is particularly critical as too high a dosage may cause hypoglycemia if too much insulin, or too little food, is taken by the patient. If hypoglycemia occurs, it must be treated through glucose administration.
In addition, control of a diabetic's blood sugar levels through, for example, once-a-day insulin injections presents the inconvenience of causing somewhat drastic rises and falls in blood sugar levels which, some diabetogists believe, could be responsible for the degeneration of blood vessels, resulting from excess blood glucose.
Insulin pump apparatus or insulin infusion pumps, have been recently developed for the treatment of hospitalized and ambulatory diabetics. The pump is connected through appropriate flexible conduits to subcutaneous needles or cannulae inserted in the abdomen, for example. Operation of the infusion pump is controlled by a microprocessor, according to a predetermined program, to inject an appropriate amount of insulin into the patient's bloodstream at appropriate intervals or, alternatively, to provide a constant insulin flow rate. An appropriate manual control is also often provided for delivering a pre-programmed dosage of insulin prior to meals for handling the blood sugar level increase following the ingestion of food.
Insulin infusion pumps have been miniaturized to the point that they are approximately of the size of a miniature radio receiver or pocket calculator, worn on a belt by ambulatory diabetics. Proper use of insulin infusion pumps requires adequate monitoring of the user's blood glucose levels, in order to avoid hypoglycemia and hyperglycemia. Monitoring of the blood glucose level permits to insure that the insulin delivery rate of the pump is neither excessive nor insufficient, and that the rate of injection of insulin is controlled as a function of the blood glucose level if such level can be determined in real time by an appropriate sensor or monitor. Unfortunately, no practical miniature blood glucose level sensing and monitoring transducer has, until the present, been developed that would permit automatic operation of a portable insulin infusion pump, without human intervention for monitoring a diabetic's blood glucose level.
Blood glucose level sensors or monitors presently available are of the chemical or of the electrolytic type. Whatever the type used they are generally complex, heavy and cumbersome, thus defeating the portability advantages of the miniaturized microprocessor controlled insulin infusion pumps. Furthermore, such sensors or monitors require that a second pair of cannulae be implanted in the patient with an appropriate flexible conduit network permitting blood to circulate through the sensor and be returned to the patient's bloodstream.
An ideal blood glucose level sensor or monitor capable of directly controlling the operation of an insulin infusion pump administrating an appropriate dosage of insulin when the blood sugar level reaches an unacceptable level, and, in addition, capable of remotely controlling a glucose infusion pump for administrating an appropriate dosage of glucose in the event that a patient's blood sugar level decreases below an acceptable level, should be preferably in the form of a relatively small transducer which could be easily implanted in the patient's bloodstream and which would be effective in operation and reliable over a long period of time, and safe in use.
The present invention provides such a sensor and monitor transducer which utilizes as principle of operation variations in blood osmostic pressure resulting from changes in blood sugar levels.
Blood osmostic pressure is a function primarily of concentration of sodium chloride, concentration of urea, and concentration of blood sugar or glucose. Under normal circumstances, the concentration of sodium chloride and the concentration of urea are constant, even in individuals affected with diabetes mellitus. The concentration of sodium chloride increases under unusual circumstances such as severe dehydration and decreases below normal also under unusual circumstances such as extreme overhydration. Concentration of urea also increases under unusual circumstances such as acute or chronic kidney failure. Absent such unusual circumstances, in a normal individual and in a diabetic individual, changes in osmostic blood pressure relate directly to rises and falls in blood glucose levels.